Equipment                                                                          Latest change 2017-10-02


In brief:
A description of the equipment made for the Chapel.

- Top mount with Hall sensors to measure the behaviour of the pendulum.
- Wire to suspend the bob.
- Bob, aluminium cylinder filled with ca. 6 kg lead.
- Base assembly allowing precise adjustment of the coil set consisting of:
  - Zero cross detection coil.
  - Drive coil.
  - Rim coil.
- Bob Control electronics to detect center and rim passages and to control the drive coil.
- PC program which takes the data from the Line Sensors and the Bob Control unit and presents it graphically and logs the data for later study.
- Analysis program to study the logged data.
- Firmware for the BobControl and Power units.

- The story of the broken cable.

With similar equipment at home I've seen a very regular behaviour of the pendulum and a Foucault precession which very good matches the calculated value for this lattitude.
The setup has no Charron ring or something equivalent, but obeys the timing requirement from Schumacher, that is, to give the drive impulse at a very particular moment in the swinging period. There is a substantial amount of ellipse, changing periodically in direction. But it has hardly any effect on the velocity of the Foucault precession.


Top mount
The Top mount is rigidly mounted to a purlin of the roof, next to the open stairs. This gave me a height of about 4.5 meters for the length of the pendulum.
In the Chapel the Top Mount is attached to a raft of the roof at approx. 8.5 m height.
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Wire
The wire at home is a piano wire of 0.75 mm diameter, in the chapel it is 0.925 mm diameter (gauge 16).
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Bob
The bob consists of an aluminium cylider filled with lead. A central rod allows it to be attached to the wire. On the lower end of this rod sits a magnet which induces electrical signals in the Zero-crossing coil and in the Rim coil, and it experiences a repelling force when the Drive Coil is engaged.
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Floor unit
The base assembly contains the Coil assembly and the mechanism for precise centering of the coil assembly
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Zero cross detection coil
This small coil at the center of the base-assembly detects the passing of the Bob. When the Bob is approaching the voltage will rise. When the Bob is nearly overhead the voltage will fall and cross zero at the moment that the bob is exactly in the center.
The Arduino software detects this center-crossing and starts the timing for a.o. the DriveCoil pulse.
When the time for one half of the swing differs from the time for the other half, our zero detection coil is not at the center of the pendulum's swing. This can be corrected with the centering mechanism. 
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Drive coil
The driveCoil, when engaged, provides a repelling force on the magnet in the Bob's lower stem. This will replenish the energy lost by air friction in each swing.
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Rim coil
The rim coil sits at a somewhat large distance from the center. Detecting the Bob's passages tells us quite precise what the amplitude of the pendulum is. Based on this information the duration of the drive pulse is modified to keep the amplitude as constant as possible.
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Bob Control Electronics
The electronics for the BobControl unit consists of some operational amplifiers to condition the signals from the Center- and Rim coils and the Hall sensors, and to engage the DriveCoil at the proper moment during the proper time. At the hart of the electronics sits an Arduino Nano. 
Here you find the zipped code for the Nano. 
Look here for the schematics and a detailed description of the electronics. 
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Power supply Electronics
The whole system is supplied from a 24 Volts battery, which is constantly charged by a mains power supply.
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PC Program
This program collects data from the Arduino processors in the BobControl unit and the Power unit, present some data graphically and logs all important data to a server in the network.It also allows to change several parameters of the Pendulum Contol.
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Analysis Program
The Analisys Program, also written in FPC and Lazarus IDE shows us the behaviour of the pendulum over somewhat longer time, as it emerges from the logfiles.
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Firmware
The Arduino firmware for the units Bob Control and Power.
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